Zinc peroxide is used as a cross-linker of a carboxyl group in production of a nitrile rubber, a deodorant, a bactericide, a bleaching agent, a curing agent, a photocatalyst and the like. Zinc peroxide may be added to fireworks etc. as an oxidant. Further, zinc peroxide turns to zinc oxide when calcinated, and therefore can also be used as an intermediate material for production of zinc oxide. As a method for production of such zinc peroxide particles, Patent Document 1 describes a method in which a precipitate of zinc hydroxide obtained by adding a basic solution to a solution containing a zinc salt is dispersed in hydrogen peroxide water, and the dispersion is subjected to a heating treatment to obtain a fine particle dispersion sol of zinc oxide.
In the production method, however, fine zinc peroxide particles having a high specific surface area are produced, and round-shaped zinc peroxide particles having an average particle diameter of 0.04 μm or more cannot be obtained. Fine zinc peroxide particles having a small particle diameter have the problem that it is difficult to form zinc oxide particles while maintaining the shape/size of zinc peroxide particles because finer particles have a stronger cohesive force, so that fusion of particles more easily proceeds when zinc oxide particles are formed by thermal decomposition. For rectifying the above-mentioned problem, zinc peroxide particles having a larger particle diameter are desired. However, such zinc peroxide particles having a large particle diameter and a method for production thereof are unknown. For arbitrarily controlling the reactivity of zinc peroxide, such as oxidizing power and photocatalytic activity, for example, a method is conceivable in which by controlling the particle diameter, the surface area of particles is controlled to control the reactivity of zinc peroxide. However, a method for controlling the particle diameter of zinc peroxide particles with high accuracy in a particle diameter region of 0.04 μm or more is unknown.
Further, zinc oxide particles are used in many applications such as ultraviolet blocking agents in cosmetics and heat releasing fillers. In these applications, fine zinc oxide particles having a particle diameter of 0.1 μm or less (for example, Patent Documents 2 and 3), and zinc oxide particles having a particle diameter of more than 1.0 μm are largely examined, but round-shaped zinc oxide particles having a particle diameter of about 0.04 to 1.0 μm are not so much examined, and a method for production thereof is not fully established. Recently, however, zinc oxide particles having the above-mentioned particle diameters have been becoming required for applications such as cosmetics and heat releasing fillers from the viewpoint of improvement of ultraviolet blocking performance, improvement of visible light transparency, use in heat releasing fillers of particles having such an intermediate size as to increase the filling rate when the particles are used in combination with a heat releasing filler having a large particle diameter, and so on.
These rounded zinc oxide particles having a particle diameter of 0.04 to 1.0 μm have a small aspect ratio and a shape close to a spherical shape, and therefore when they are used as a heat releasing filler in combination with particles having a large particle diameter for the purpose of enhancing thermal conduction, thermal conduction can be enhanced more efficiently than when zinc oxide particles, which have a similar particle size but do not have a rounded shape, are compounded.